1. Field of the Disclosure
The present disclosure relates generally to the photovoltaic generation of electrical energy. The present disclosure relates more particularly to photovoltaic roofing products for use in photovoltaically generating electrical energy.
2. Technical Background
The search for alternative sources of energy has been motivated by at least two factors. First, fossil fuels have become increasingly expensive due to increasing scarcity and unrest in areas rich in petroleum deposits. Second, there exists overwhelming concern about the effects of the combustion of fossil fuels on the environment due to factors such as air pollution (from NOx, hydrocarbons and ozone) and global warming (from CO2). In recent years, research and development attention has focused on harvesting energy from natural environmental sources such as wind, flowing water, and the sun. Of the three, the sun appears to be the most widely useful energy source across the continental United States; most locales get enough sunshine to make solar energy feasible.
Accordingly, there are now available components that convert light energy into electrical energy. Such “photovoltaic cells” are often made from semiconductor-type materials such as doped silicon in either single crystalline, polycrystalline, or amorphous form. The use of photovoltaic cells on roofs is becoming increasingly common, especially as system performance has improved. They can be used, for example, to provide at least a significant fraction of the electrical energy needed for a building's overall function; or they can be used to power one or more particular devices, such as exterior lighting systems and well pumps.
Accordingly, research and development attention has turned toward the development of photovoltaic products that are adapted to be installed on a roof. While stand-alone photovoltaic modules have been in use for some time, they tend to be heavy and bulky, and aesthetically unfavorable when installed on a roof. Roofing products having photovoltaic cells integrated with roofing products such as shingles, shakes or tiles, or roofing panels have been proposed. Examples of such proposals have been disclosed in U.S. Patent Application Publications nos. 2006/0042683A1, 2008/0149163A1, 2010/0313499A1 and 2010/0313501A1, and in U.S. Pat. No. 4,040,867, each of which is hereby incorporated by reference herein in its entirety. A plurality of such photovoltaic roofing elements (i.e., including photovoltaic media integrated with a roofing product) can be installed together on a roof, and electrically interconnected to form a photovoltaic roofing system that provides both environmental protection and photovoltaic power generation. These can be very advantageous, but can be difficult to install on steep surfaces, while ensuring sufficient closure of the roof against the elements, particularly wind driven rain, and can often result in incomplete coverage of the roof surface with photovoltaic power generation. Moreover, as it is often desirable to have photovoltaic roofing elements covering a portion of a roof surface and conventional roofing products covering the remainder of the surface, there is a need for systems that provide aesthetic effect in the transition zone between the conventional roofing products and the photovoltaic roofing elements while closing the roof and the array of photovoltaic roofing elements to the environment.
Photovoltaic roofing systems are often installed together with a conventional roof covering (i.e., of non-photovoltaic roofing elements) such that rows of the various elements disposed toward the top end of the roof deck overlap rows disposed more toward the bottom end of the roof deck. In such an arrangement, the bottom row of photovoltaic roofing elements would typically overlap the headlap zones of the non-photovoltaic roofing elements immediately down-roof as such, in such installations, the non-photovoltaic roofing elements toward the bottom end of the roof deck must typically be installed on the roof before the photovoltaic roofing elements. This can be especially complicated in installations in which non-photovoltaic roofing elements are to be installed to overlap flashings associated with the photovoltaic roofing elements, as it would require non-photovoltaic roofing elements to be installed both before and after installation of the photovoltaic roofing elements. Moreover, replacement of the non-photovoltaic roofing elements disposed under the bottom row of photovoltaic roofing elements (e.g., as part of re-covering the roof with new shingles) can be complicated by the fact that the fasteners affixing them to the roof deck are covered by the photovoltaic roofing elements.
There remains a need for photovoltaic products that address one or more of these deficiencies.